Lubrication system for crankshaft

ABSTRACT

A lubrication system for a crankshaft, which is capable of improving the durability of the crankshaft, is provided. The crankshaft is rotatably mounted in a crankcase and is connected to a piston via a connecting rod. The crankshaft has a journal portion and a crank web integrally provided therewith, wherein a crankpin is provided on the crank web. A lubricating oil-supply path is formed in the crankshaft, and an opening of the lubricating-oil supply path is formed on an end face of the crank web so as to face to an end portion of a bearing. The lubricating oil discharged from the opening is supplied to the bearing through an end portion of the bearing, and the opening for discharging the lubricating oil is not formed on an outside periphery of the crankpin. Therefore, the outside periphery becomes wholly flat.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a lubrication system for acrankshaft, which is lubricated between a crankpin of the crankshaft anda connecting rod.

[0002] An engine includes a piston reciprocating in a cylinder, and acrankshaft rotatably mounted in a crankcase, wherein a piston and thecrankshaft are connected through a connecting rod. To supply lubricatingoil to contact portions of respective members constituting the engine,an oil pump is driven by the crankshaft. In a four-cycle engine, thelubricating oil from the oil pump is supplied also to contact portionsbetween a crankpin of the crankshaft and a bearing incorporated in anend portion of the connecting rod.

[0003] In an assembly-type crankshaft formed by a plurality of membersso that they are linked through the crankpin, a hollow crankpin can beused. Thus, in the crankshaft using the hollow crankpin, as described inpatent document 1, a communication hole for communicating with a hollowhole and an outside periphery of the crankpin is formed in a diameterdirection thereof, and the lubricating oil from the oil pump issupplied, through the hollow hole and the communication hole, to acontact portion between a rolling bearing fitted to the crankpin and thecrankpin, whereby the lubricating oil is directly discharged into anoutside periphery of a rotating body of the rolling bearing.

[0004] Meanwhile, in a connecting rod of such a type that a slidingbearing is incorporated between the crankshaft and an end portion of acrankshaft side of the connecting rod, as described in patent document2, a supply hole of the lubricating oil is formed in the connecting rodso as to communicate with an inner surface of the sliding bearing and aninner surface of a fitting hole to which a piston pin is fitted.

[0005] [Patent Document 1]

[0006] Japanese Patent Laid-Open (TOKUKAIHEI) No. 7-119428

[0007] [Patent Document 2]

[0008] Japanese Patent Laid-Open (TOKUKAIHEI) No. 5-106630

SUMMARY OF THE INVENTION

[0009] As described above, to supply the lubricating oil to the contactportion between the crankpin and the bearing fitted thereto, durabilitytests have been performed for the engine provided with the crankshaft inwhich an opening of a lubricating-oil supply path is formed on theoutside periphery of the crankpin so as to face to an inner surface ofthe bearing. As a result of observation of the crankshaft after drivingthe engine over a long term, it has been found out that a flakingphenomenon occurs at a fringe, i.e., an edge of the opening of thelubricating-oil supply path formed in the crankpin. This flakingphenomenon is one in which the fringe of the opening is worn away, andif the flaking phenomenon occurs, the lubricating oil cannot beappropriately supplied to the contact portion.

[0010] Investigations of the reason for the occurrence of the flakingphenomenon have shown that when a rolling bearing such as a rollerbearing is mounted to the crankpin, a rotating body such as a roller ofthe rolling bearing rolls and contacts to the outside periphery of thecrankpin, whereby a surface pressure applied to the outside periphery ofthe crankpin from this rotating body is such that the fringe of theopening is several times higher in the surface pressure than otherportions. Thus, it is thought that when the high surface pressure isapplied to the fringe of the opening, the flaking phenomenon occurs atthe fringe at the very first due to the high surface pressure. If theflaking phenomenon occurs at the fringe at the very first, desiredlubrication performance cannot be maintained even though there are nodefects in other parts, and so the durability of the crankshaft is lost.

[0011] An object of the present invention is to provide a lubricationsystem for a crankshaft, which is capable of improving the durability ofthe crankshaft.

[0012] A lubrication system for a crankshaft according to the presentinvention is one which lubricates a connecting portion between acrankshaft rotatably mounted in a crankcase and connected to a piston ina cylinder via a connecting rod and said connecting rod, saidlubrication system comprising: a crankpin attached to a crank webintegrally provided with a journal portion to form said crankshaft; abearing mounted on an end portion of said connecting rod and fitted tosaid crankpin; and a lubricating-oil discharging opening communicatingwith a lubricating-oil supply path formed in said crankshaft, saidopening being formed on an end face of said crank web, wherein thelubricating oil is discharged from said opening to an end portion ofsaid bearing.

[0013] In the lubrication system of a crankshaft according to thepresent invention, said bearing is a rolling bearing having a rotatingbody. Further, in the lubrication system of a crankshaft according tothe present invention, said crankshaft is formed by: a plurality ofshaft elements each having a journal portion and a crank web integrallyformed therewith; and a crankpin connecting the shaft elements attachedto an attachment hole formed in each of the crank webs, and connectingthe crank elements.

[0014] In the present invention, since the opening of thelubricating-oil supply path formed in the crankshaft is formed on theend face of the crank web, the lubricating oil can be supplied, throughthe end portion of the bearing, to the sliding portion between thebearing fitted to the crankpin and the crankpin. Therefore, it isunnecessary to form the opening of the lubricating-oil supply path onthe outside periphery of the crankpin, and the surface pressure appliedto the crankpin from the bearing becomes almost uniform over theentirety of the outside periphery of the crankpin. Accordingly, withoutthe occurrence of the flaking phenomenon on the outside periphery of thecrankpin, the durability of the crankshaft can be improved.

DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a schematic diagram showing an engine in which alubrication system for a crankshaft according to an embodiment of thepresent invention is incorporated.

[0016]FIG. 2 is an enlarged sectional view showing a part of FIG. 1.

[0017]FIG. 3 is a perspective view showing one shaft elementconstituting a crankshaft.

[0018]FIG. 4 is a sectional view showing a part of a crankpin and aconnecting rod as a comparison example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will bedescribed in detail based on the drawings. FIG. 1 is a schematic diagramshowing an engine in which a lubrication system for a crankshaftaccording to an embodiment of the present invention is incorporated, andFIG. 2 is an enlarged sectional view showing a part of FIG. 1.

[0020] This engine is a four-cycle single-cylinder one and can beapplied as an engine of a vehicle such as a buggy, more specifically,applied as an engine of an ATV, namely, all-terrain vehicle. As shown inFIG. 1, this engine includes a crankcase 12 rotatably supportingcrankshafts 11, and a piston 14 reciprocally incorporated in a cylinder13 mounted in the crankcase 12. To transmit the reciprocating motion ofthe piston 14 to the rotary motion of the crankshaft 11, a connectingrod 17 is connected between a piston pin 15 fixed to the piston 14 and acrankpin 16 fixed to the crankshafts 11.

[0021] A cylinder head 18 is attached to the cylinder 13, and thecylinder head 18 and the piston 14 form a combustion chamber 19 in thecylinder 13. A suction port communicating with the combustion chamber 19and supporting an air-fuel mixture and an exhaust port exhausting ancombustion gas are formed in the cylinder head 18. An not shown suctionvalve for opening/closing the suction port and an not shown exhaustvalve for opening/closing the exhaust port are formed in the cylinderhead 18, respectively. To open/close-drive the suction valve and theexhaust valve, a camshaft 20 is rotatably attached to the cylinder head18, and a sprocket 21 fixed to the camshaft 20 is connected to asprocket 22 fixed to the crankshaft 11 via a chain 23. Therefore, thecamshaft 20 is driven by the crankshaft 11.

[0022] A rocker shaft 24 parallel to the camshaft 20 is rotatablymounted in the cylinder head 18, and a rocker arm 25 foropen/close-driving the suction valve and a rocker arm 26 foropen/close-driving the exhaust valve are rotatably mounted on the rockershaft 24. One end portions of the rocker arms 25 and 26 come in contactwith valve-operating cams 27 and 28, respectively, and the suction valveand the exhaust valve are attached to the other end portions thereof.

[0023] In the engine shown in FIG. 1, a generator case 31 is attached tothe crankcase 12, and a generator 32 is mounted in this generator case31. The generator 32 includes an outer rotor 34 provided with magnets 33and a stator 36 provided with coils 35, wherein the outer rotor 34 isfixed to the crankshaft 11 and the stator 36 is fixed to the generatorcase 31. The electric power generated by the rotation of the crankshaft11 is supplied to an not shown battery from this generator 32, wherebythe battery is charged.

[0024] As shown in FIG. 2, the crankshaft 11 is rotatably mounted in thecrankcase 12 by bearings 37 and 38 attached to the crankcase 12. Thecrankshaft 11 shown in FIG. 2 has two shaft elements 11 a and 11 b, andone shaft element 11 a is shown in FIG. 3. As shown in FIG. 3, the shaftelement 11 a is provided with a journal portion 41 a rotatably supportedby the bearing 38, and a crank web 42 a integrally formed with an endportion of the journal portion 41 a. The crank web 42 a has a crank armportion 43 a protruding in a diameter direction, and a balance weightportion 44 a protruding in a direction opposite to that of the crank armportion 43 a, wherein an attachment hole 45 a is formed in the crank armportion 43 a. Similarly, also in the other shaft element 11 b, a crankweb 42 b integrally provided with a journal portion 41 b includes acrank arm portion 43 b and a balance weight portion 44 b, wherein anattachment hole 45 b is formed in the crank arm portion 43 b.

[0025] The crankshaft 11 is formed, by coupling the two shaft elements11 a and 11 b through the crankpin 16 fitted into the attachment holes45 a and 45 b, and the crankpin 16 has a communication hole 47 thereinand so becomes hollow. In the connecting rod 17 connecting thecrankshaft 11 and the piston 14, a link end portion 49 having a fittinghole 49 a to which the piston pin 15 fixed to the piston 14 is fitted isprovided on one end thereof. In a link end portion 51 provided at theother end thereof, a fitting hole 51 a to which a bearing 50 fitted tothe crankpin 16 is fitted is formed. The bearing 50 is provided with aplurality of rotating bodies such as rollers 52, and a retainer 53having a groove rotatably accommodating the respective rollers 52.

[0026] A lubricating-oil supply path 55 having an opening 54 on an endface of the crank web 42 a is formed in the shaft element 11 a of thecrankshaft 11, and the lubricating-oil supply path 55 communicates withan not shown discharge port of the oil pump. The lubricating-oil supplypath 55 and the discharge port of the oil pump may communicate with eachother through an oil path formed in the crankcase 12, or through a jointportion provided at the end portion of the crankshaft 11. The opening 54of the lubricating-oil supply path 55 is formed so as to face to an endface of the bearing 50. The lubricating oil discharged from the oil pumpserving as a lubricating-oil supply source is supplied into the insideof the bearing 50 from a side of the end portion of the bearing 50, andthe outside periphery of the crankpin 16 and the roller 52 rolling alongthe outside periphery thereof are contacted via an oil film.

[0027] The lubricating-oil supply path 55 communicates with thecommunication hole 47 in the crankpin 16, through a communication oilpath 56 formed in the crankshaft 11 and a communication hole 56 a formedin the crankpin 16 so as to communicate with the oil path, whereby thelubricating oil is supplied to the communication hole 47. Plugs 57 a and57 b are fixed at both ends of the communication hole 47 of the crankpin16, and a discharge hole 58 for supplying the lubricating oil to thebearing 37 is formed in the plug 57 a. However, if the lubricating oilcan be supplied to the bearing 37 through the other oil path, it isunnecessary to provide the communication oil path 56 and thecommunication hole 47.

[0028] As described above, the opening for discharging the lubricatingoil is not formed in a partial one on which the roller 52 rolls in theentire outside periphery of the crankpin 16, whereby the outsideperiphery of the crankpin 16 becomes wholly flat. As a result, withoutlocally increasing the surface pressure at the outside periphery of thecrankpin 16 by loads applied from the roller 52, the wholly uniformsurface pressure is applied to the outside periphery of the crankpin 16.Therefore, the flaking phenomenon on the outside periphery of thecrankpin 16 does not occur even after the engine has been used over along term, whereby the durability of the crankshaft 11 can be improved.

[0029]FIG. 4 is a sectional view showing a part of the crankpin 16 andthe connecting rod 17 as a comparison example. In this comparisonexample, to supply the lubricating oil to the bearing 50 from thecommunication hole 47 similarly to the conventional ones, alubricating-oil supply path 60 opening to the outside periphery of theroller 52 of the bearing 50 is formed in the crankpin 16. When thelubricating-oil supply path 60 is thus formed in the crankshaft 16 byopening to the outside periphery of the roller 52, the roller 52contacts to a fringe of such an opening with some large surfacepressure. Therefore, a flaking phenomenon 61 occurs at the fringe of theopening due to secular change in the crankpin 16, and the lubricationperformance is changed. However, such a flaking phenomenon does notoccur in the crankshaft 11 of the present invention, whereby thedurability of the crankshaft 11 can be improved.

[0030] The present invention is not limited to the above-mentionedembodiment, and can be variously modified and changed without departingfrom the gist thereof. For example, the crankshaft 11 illustrated in thedrawings is for the single-cylinder engine. However, the presentinvention can also be applied to a crankshaft for multi-cylinder engine.Further, the engine provided with the crankshaft 11 can be applied as anengine for motorcycle or a multi-purpose engine for generator besidesthe ATV. Furthermore, the crankshaft 11 illustrated in the drawings isof such an assembly type as to connect the shaft elements 11 a and 11 bthrough the crankpin 16. However, it is also possible to apply thepresent invention to a crankshaft of an integrally formed type.Additionally, a needle bearing can be used as the rolling bearing aswell as the roller bearing.

[0031] According to the present invention, since the opening of thelubricating-oil supply path formed in the crankshaft is formed on theend face of the crank web, it is possible to supply the lubricating oilto the sliding portion between the bearing fitted to the crankpin andthe crankpin, through the end portion of the bearing. Therefore, withoutthe occurrence of the flaking phenomenon on the outside periphery of thecrankpin, the durability of the crankshaft can be improved.

[0032] The entire disclosure of a Japanese Patent Application No.2003-087522, filed on Mar. 27, 2003 including specification, claims,drawings and summary, on which the Convention priority of the presentapplication is based, are incorporated herein by reference in itsentirety.

What is claimed is:
 1. A lubrication system for a crankshaft, whichlubricates a connecting portion between a crankshaft rotatably mountedin a crankcase and connected to a piston in a cylinder via a connectingrod and said connecting rod, said lubrication system comprising: acrankpin attached to a crank web integrally provided with a journalportion to form said crankshaft; a bearing mounted on an end portion ofsaid connecting rod and fitted to said crankpin; and a lubricating-oildischarging opening communicating with a lubricating-oil supply pathformed in said crankshaft, said opening being formed on an end face ofsaid crank web, wherein the lubricating oil is discharged from saidopening to an end portion of said bearing.
 2. The lubrication systemaccording to claim 1, wherein said bearing is a rolling bearing having arotating body.
 3. The lubrication system according to claim 1, whereinsaid crankshaft is formed by: a plurality of shaft elements each havinga journal portion and a crank web integrally formed therewith; and acrankpin connecting the shaft elements attached to an attachment holeformed in each of the crank webs, and connecting the crank elements. 4.The lubrication system according to claim 2, wherein said crankshaft isformed by: a plurality of shaft elements each having a journal portionand a crank web integrally formed therewith; and a crankpin connectingthe shaft elements attached to an attachment hole formed in each of thecrank webs, and connecting the crank elements.